National Health and Nutrition Examination Survey

Both the lab data and questionnaire items will be released in this file.

Volatile Organic Compound Questions

The volatile organic compound section of the Mobile Examination Center (MEC) Interview and Phlebotomy Component (PH) provide personal interview data.

Volatile Organic Compounds (Whole Blood) - Trihalomethanes/MTBE/Nitromethane

Volatile organic compounds (VOCs) are a large group of chemicals that have been used as solvents, degreasers, and cleaning agents in industry and consumer products. Many of the VOCs were found to contaminate ground water and drinking water sources, and because of human health concerns, have been banned or restricted from most uses.

The prevalence of disinfection by-products in drinking water supplies has raised concerns about possible adverse health effects from chronic exposure to these potentially carcinogenic compounds. Methyl-tert-butyl ether (MTBE) was used as an additive to replace lead in gasoline, but its use was banned after widespread ground water contamination was discovered.

Inhalation is the most common VOC route of exposure in the general population, including: indoor sources, such as paints, adhesives, cleaning solutions, and aerosolized insecticide sprays; industries producing these solvents; and contaminated waste disposal sites. Drinking water may contribute to exposure when underground drinking water supplies are contaminated. After they are absorbed in the body, VOCs are rapidly eliminated in exhaled breath, or may be rapidly metabolized and eliminated in the urine.

Examined participants aged 12 years and older from a one-half sample were eligible.

Interview Setting and Mode of Administration
The questions were asked during the physical examination, in the mobile examination center (MEC). The questions were administered by the phlebotomist or the MEC interviewers.

Laboratory Methodology
Trihalomethanes (THMs), nitromethane (NM: biomarker for halonitromethanes), and methyl tert-butyl ether (MTBE) are measured in whole blood by solid phase microextraction/gas chromatography/isotope dilution mass spectrometry (SPME/GC/isotope dilution MS) based on the method described by Bonin, et al. The method is applicable to the determination of five VOCs in 3-mL samples of whole blood with detection limits in the low parts per trillion (pptr) range. Since non-occupationally exposed individuals have blood VOC concentrations in this range, the method is applicable for determining these quantities and investigating cases of low-level exposure to VOCs.

Refer to the Laboratory Method Files section for detailed laboratory procedure manual(s) of the methods used.

There were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2007-2008 cycle.

Trihalomethanes/MTBE/Nitromethane (May 2016)

Whole blood specimens were processed, stored, and shipped to Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA for analysis.

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate refrigerated (2-8°C) conditions until they are shipped to National Center for Environmental Health, for testing.

The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES LPM.

Mobile Examination Centers (MECs)

Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured quality assurance evaluation during unscheduled visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff member is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff member. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.

Analytical Laboratories

NHANES uses several methods to monitor the quality of the analyses performed by the contract laboratories. In the MEC, these methods include performing blind split samples collected on “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2% of all specimens.

NCHS developed and distributed a quality control protocol for all the contract laboratories which outlined the use of Westgard rules (Westgard et al., 1981) when running NHANES specimens. Progress reports containing any problems encountered during shipping or receipt of specimens, summary statistics for each control pool, QC graphs, instrument calibration, reagents, and any special considerations are submitted to NCHS quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.

All QC procedures recommended by the manufacturers were followed. Reported results for all assays meet the CDC/NCEH Tobacco and Volatile Branch quality control and quality assurance performance criteria for accuracy and precision, similar to the Westgard rules (Caudill et al., 2008).

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Refer to the 2007-2008 Laboratory Data Overview for general information on NHANES laboratory data.

Subsample Weights
Whole blood VOCs were measured in a one-half subsample of persons 12 years and older. Special sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data.

Some records have a 0 weight because additional VOC results were obtained after the construction of the sample weights for this component. For assistance in modifying the weights for analysis, please contact DHANES.

Demographic and Other Related Variables

The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2007-2008 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.

The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture.

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).

Detection limits

The detection limits were constant in the data set. Two variables are provided for each of these analytes. The variable name ending in “LC” (ex., LBDVBFLC) indicates whether the result was below the limit of detection: “0” means that the result was at or above the limit of detection, “1” indicates that the result was below the limit of detection. For analytes with analytic results below the lower limit of detection (ex., LBDVBFLC=1), an imputed fill value was placed in the analyte results field. This value is the lower limit of detection divided by square root of 2 (LLOD/sqrt [2]). The other variable prefixed LBX (ex., LBXVBF) provides the analytic result for that analyte.